I'm not sure why anyone else hasn't mentioned it, but I found the part about the Tezuman Empire to be a riot. Then again, I must confess to be something of an "amateur expert" on pre-Columbian (or, to be more precise, pre-Cortesian) Mesoamerican cultures. So.
I always loved this bit:
Terry Pratchett wrote:"I'm going to complain about this, demon," moaned Eric. "You just wait till my mother finds out. My parents have got influence, you know."
"Oh, good," said Rincewind weakly. "Why don't you tell the high priest that if he cuts your heart out, she'll be right down to the school tomorrow to complain."
Not to mention Quezovercoatl. What a pun!
The parody of the Trojan war is also well done, and I like the bit about "living forever". However, the highlight for me is the trip through hell. All in all, a fairly enjoyable (if short) book - but I can understand that, with three other books coming out in the same year, Pterry presumably didn't have time to devote his full attention to this one. Oh well!
By the way, this one gains enormously
from Stephen Briggs's adaptation on audiobook (as do them all, but particularly this one). I consider Stephen's adaptation to be far superior to Tony Robinson's, mainly because Tony's adaptations are always cut heavily to fit on three CDs, which means that a lot of funny material is cut. However, the early books (read by Nigel Planer) are also very well done, and usually much more whimsical. Despite this, Stephen brings some much-needed gravitas to his portrayal of Vetinari and Death - whereas Nigel's Death sounds vaguely like a parody of Himself, with lots of echo.
Anyway, that's my (relatively) short review of Eric